1. Field of the Invention
This invention is concerned with the management of a human airway in order to control respiration. More particularly, the invention concerns a device that couples an airway tube reliably and safely with the laryngeal opening, the upper end of the trachea, which is the breathing passageway that leads to the lungs. The device seats in the throat immediately adjacent the laryngeal opening, tensions and erects the laryngeal opening, and seals within the laryngeal opening to provide a channel through the airway tube for artificial ventilation of the lungs.
2. Prior Art
The airway of a human being includes the throat and windpipe, and leads to the lungs. Control and management of a patient's airway are required under a variety of circumstances. During the administration of general anesthesia, in particular, the resultant loss of consciousness and muscle tone require that patient ventilation be maintained through an artificial airway. Control of a patient's airway is also necessary to permit mechanical ventilation of a patient with diseased or injured lungs and during resuscitation of a hemodynamically compromised and apneic or non-breathing patient. Mechanical ventilation of a patient involves forming a seal about some portion of the patient's breathing anatomy and introducing air that varies in pressure through the seal. The air is provided through a tube from a ventilating machine. The seal confines the varying air pressure in the airway and lungs of the patient, imposing an artificial respiration on the lungs. A breach in the seal undesirably lets the varying pressure escape to the ambient atmosphere, which inhibits airway management. Therefore, the quality and efficacy of an airway management device depends upon the seal that it forms where it interfaces with a patient's airway.
A wide variety of devices are currently available to manage a patient's airway. For simplicity, these airway devices can be categorized as follows: face masks, tracheal tubes and pharyngeal airways.
A face mask covering the mouth and nose and with a port for connection to a ventilation means is commonly used for short term control of the airway. The face mask is non-invasive in that sealing of the airway is accomplished not by penetration into the patient's airway, but rather by skin contact, with the mask encircling the mouth and nose. However, airway patency is not assured since the tongue and other structures can obstruct the airway. Also, it is difficult to maintain a seal of the airway for any period of time, particularly during positive pressure ventilation. Leakage around the face mask results in ineffective ventilation and, during anesthesia, contaminates the operating room with anesthetic gases. Furthermore, a face mask does not prevent the introduction of air into the esophagus and stomach (gastric insufflation) or protect against the aspiration of stomach contents (breathing of vomited material). Still further, the face mask precludes surgical field avoidance during oral, nasal and facial procedures, and it is inappropriate for patients with facial burns.
Tracheal tubes (also called endotracheal tubes and ETTs) are inserted through the mouth or nose and into the trachea (the windpipe) where an inflatable balloon or cuff surrounding the tube seals against the interior surface of the trachea. This approach avoids the deficiencies of face masks because it includes the provision of a conduit traversing the pharynx, and forms an effective seal against the airway, allowing positive pressure ventilation, and protection against aspiration of stomach contents. However, while solving several problems, tracheal tubes create new challenges. They are difficult to insert and position properly within the trachea, almost always requiring a laryngoscope, stylet or other intubation aid. Penetration of the larynx and trachea is invasive and is a highly noxious stimulus requiring a deep plane of anesthesia. Furthermore, once in place, tracheal tubes injure the delicate tissue of the larynx and trachea including the vocal cords. Incorrect positioning of the tube tip (distally into the mainstem bronchi or proximal dislocation out of the trachea) is an additional concern.
Another method of ensuring a patent airway is to insert a tracheostomy tube through an opening in the front of the neck and directly into the trachea. This approach is even more invasive than the tracheal tube in that it requires surgery to install the tube; consequently, it is reserved for patients chronically requiring ventilatory assistance or for those needing emergency relief from an obstructed upper airway.
With the current trend toward minimally invasive surgery, the concept of an airway management device with a supraglottic seal without the stimuli of tracheal intubation has widespread appeal. A supraglottic seal seals in the throat, above the larynx, while providing a passageway to the laryngeal opening through which ventilatory gases may be delivered. Since these devices normally terminate in the pharynx, the portion of the throat from the mouth to the larynx, they are commonly referred to as "pharyngeal" devices. When combined with a breathing tube, a pharyngeal device is called a "pharyngeal airway" device.
A variety of pharyngeal airway devices have been developed for assistance in maintaining a human airway. Some oro-pharyngeal airway devices are useful in displacing the tongue or as bite blocks, but are incapable of maintaining the airway by themselves, since a seal is not effected. Other devices include a tube with a cuff to seal against the pharyngeal wall at the base of the tongue, and with another cuff that seals around the plugged distal end of a tube situated in the esophagus. Patient ventilation occurs through side holes in the tube between the two cuffs, the side holes aligned with the laryngeal opening.
Another pharyngeal airway device includes a tube with an inflatable cuff surrounding its distal end. The cuff is intended to seal against the pharyngeal wall, above the epiglottis.
Generally, pharyngeal airway devices seal against pharyngeal structures surrounding the larynx, and merely mask or cover the larynx, rather than sealing within or directly against it. These devices characteristically form inadequate seals that leak with a moderate level of positive pressure ventilation. Further, these devices provide easily breached or imperfect barriers between the esophagus and trachea, allowing gastric insufflation and/or aspiration of stomach contents. Also, these devices usually include air channels with small bores that limit the size of tracheal tubes that can be inserted into a trachea, should intubation be desired.
The inadequate sealing performance of pharyngeal airway devices is not surprising considering their designs and the anatomy with which they interface. The larynx ("voice box") is the most proximal part of the trachea and opens into the pharynx, immediately behind the base of the tongue. The adult laryngeal inlet (the opening into the larynx and trachea) looks very similar to a piece of pipe, approximately 5/8" in diameter with its end beveled at an approximately 30.degree. angle. The pipe analogy is accurate when describing the general appearance of the trachea and larynx, however it is not an accurate analogy of the functional anatomy. The laryngeal inlet is not a rigid structure. The anterior wall of the laryngeal inlet (the side facing the tongue), including the tip of the beveled end of the inlet, is formed by the epiglottis, which is a flexible cartilage. The epiglottis provides some structure to the laryngeal inlet but is sufficiently flexible that it can easily be bent posteriorly, away from the tongue, to fully cover and block the inlet. The distal posterior aspect of the laryngeal inlet is formed by two small, movable arytenoid cartilages. Finally, the side walls of the laryngeal inlet are formed by very flexible quadrangular membranes attached to the arytenoid cartilages posteriorly and to the epiglottis anteriorly. The proximal edges of the quadrangular membranes become the aryepiglottic folds that form the rim of the laryngeal inlet. It is obvious that this combination of flexible cartilages and membranes creates an inlet to the airway that is structurally strong with respect to tension and stretching, but that has virtually no structural strength with respect to compression. Radially compressive forces applied to the laryngeal inlet will easily collapse the inlet into itself, thereby covering and blocking the airway. Manifestly, radially compressive forces could not possibly form a seal against the compressible laryngeal inlet.